linux-kernel - [PATCH] Fix EDD3.0 data verification.

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Date:	Wed, 2 Feb 2011 13:21:39 +0200
From:	Gleb Natapov <gleb@...hat.com>
To:	linux-kernel@...r.kernel.org
Cc:	"H. Peter Anvin" <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>, x86@...nel.org
Subject: [PATCH] Fix EDD3.0 data verification.

Check for nonzero path in edd_has_edd30() has no sense. First, it looks
at the wrong memory. Device path starts at offset 30 of the info->params
structure which is at offset 8 from the beginning of info structure, but
code looks at info + 4 instead. This was correct when code was introduced,
but around v2.6.4 three more fields were added to edd_info structure
(commit 66b61a5c in history.git). Second, even if it will check correct
memory it will always succeed since at offset 30 (params->key) there will
be non-zero values otherwise previous check would fail.

The patch replaces this bogus check with one that verifies checksum.

Signed-off-by: Gleb Natapov <gleb@...hat.com>
diff --git a/arch/x86/boot/edd.c b/arch/x86/boot/edd.c
index c501a5b..6c1ac02 100644
--- a/arch/x86/boot/edd.c
+++ b/arch/x86/boot/edd.c
@@ -97,6 +97,13 @@ static int get_edd_info(u8 devno, struct edd_info *ei)
 
 	/* Extended Get Device Parameters */
 
+	/*
+	 * The sum of bytes 30-73 in params structure should be zero after
+	 * int13 call. Set them to 1 to catch the case when bios works
+	 * according to phoenix spec and return 66 bytes. If we left them
+	 * to be zero, checksum will not catch that data is in wrong format.
+	 */
+	memset(&ei->params.key, 1, 74);
 	ei->params.length = sizeof(ei->params);
 	ireg.ah = 0x48;
 	ireg.si = (size_t)&ei->params;
diff --git a/drivers/firmware/edd.c b/drivers/firmware/edd.c
index 96c25d9..5e3baac 100644
--- a/drivers/firmware/edd.c
+++ b/drivers/firmware/edd.c
@@ -531,8 +531,8 @@ static int
 edd_has_edd30(struct edd_device *edev)
 {
 	struct edd_info *info;
-	int i, nonzero_path = 0;
-	char c;
+	int i;
+	u8 csum = 0;
 
 	if (!edev)
 		return 0;
@@ -544,16 +544,11 @@ edd_has_edd30(struct edd_device *edev)
 		return 0;
 	}
 
-	for (i = 30; i <= 73; i++) {
-		c = *(((uint8_t *) info) + i + 4);
-		if (c) {
-			nonzero_path++;
-			break;
-		}
-	}
-	if (!nonzero_path) {
+	for (i = 30; i <= 73; i++)
+		csum += *(((u8 *)&info->params) + i);
+
+	if (csum)
 		return 0;
-	}
 
 	return 1;
 }
--
			Gleb.
--
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